I used 2X DGX from a friend with 7D + EF 300mm f/4L My 7D was able to focus at f/8 without problems; my test was very short so I dont know anything about AF speed but it focused acurately. I noticed that all the photos I took the f-stop was reported f/4 on the photos and never changed regardles of light (I used Tv mode) but the ISO changed to adjust to different light.

This is what I read, too and it's the reason I ordered it at all: The dgx betrays the camera into thinking it's not there, and thus the f8 af works because the camera doesn't recognize it as f8... I'll report back once I've got mine, could take a bit because it's mail order.

Sorry if I've spread wrong information, but this is what I've read when shopping for Kenko as the difference between dg and dgx - so I'm not the only one mistaken. After some more quick research, it seems the dgx reports the modified _focal_lenght_ better than the dg. And what's more, some say that only the dgx allows af with f8 while the dg does not - can you acknowledge this?

Now I'm really confused. I had never tried using the 2x on an f/4 lens before, so at your request, I pulled out the 2X and my 24-105 f/4 L and put them on the Mark 3. Low and behold, it let me turn the aperture down to f/4 instead of maxing it out at f/8??? I did try a bit of AF and it seemed to work, just not really fast (I'm sitting in a semi-dark room, so probably work OK outside). Seemed to work better at the longer focal lengths as well. Now, after reading your post about thinking the DG does not report aperture, I put my 70-200 f/2.8L back on the camera with the TC and sure enough, it wouldn't go over f/5.6. So maybe it has "smart" electronics in it to allow it to AF at f/8 by not reporting the aperture, while also allowing it to report the correct aperture with a lens that's fast enough to support it?

Sorry if I've spread wrong information, but this is what I've read when shopping for Kenko as the difference between dg and dgx - so I'm not the only one mistaken. After some more quick research, it seems the dgx reports the modified _focal_lenght_ better than the dg. And what's more, some say that only the dgx allows af with f8 while the dg does not - can you acknowledge this?

Now I'm really confused. I had never tried using the 2x on an f/4 lens before, so at your request, I pulled out the 2X and my 24-105 f/4 L and put them on the Mark 3. Low and behold, it let me turn the aperture down to f/4 instead of maxing it out at f/8??? I did try a bit of AF and it seemed to work, just not really fast (I'm sitting in a semi-dark room, so probably work OK outside). Seemed to work better at the longer focal lengths as well. Now, after reading your post about thinking the DG does not report aperture, I put my 70-200 f/2.8L back on the camera with the TC and sure enough, it wouldn't go over f/5.6. So maybe it has "smart" electronics in it to allow it to AF at f/8 by not reporting the aperture, while also allowing it to report the correct aperture with a lens that's fast enough to support it?

Weird results, but hope it helps you.

YESSS! That is good! I dont need to wait for 7D MII. Just use 5D MKII with Kenko 1.4 or 2x to get the crop, and since ISO noise is very low I expect to get good photos... But wait, still dont know how fast will it focus for something like bird in flight! I will report on these issues when I get my 5D ank Kenko.

Indeed, that's why I made triple-sure to get the one that works with f8 af on the 60d. But apart from the different models, as I wrote there might be even different versions of the same model, the "Kenko Digital Teleplus Pro300 1.4x DGX for Canon EOS" model number "K1.4PRO.300DGX-C". Maybe they just changed the packaging, but maybe they silently adjusted their firmware, too:

I just did a quick experiment using my Kenko 1.4X Teleplus Pro 300 and my 70-300 f/4-5.6L IS USM lens set on Av priority at 5.6 which was the most open I could go with the convertor on with the lens at 300mm. These shots were taken hand held and with Auto ISO. The first is an attempt at autofocus. The lens kept searching and occasionally signaled that AF was reached. The first picture gave an signal that focus was reached but the indicator in the view finder flicked off but there was not change in the image in the VF. Here is that shot:

Here's a shot that was manually focused. I think it looks a little sharper to my eye:

So with my little test, it looks as if the Kenko failed. It really struggled to lock on ??maybe a firmware update would corrected this??? I am not quite sure how. Also, the fact that it was hand held and not on a tripod and with either mirror lock or 2 second delay to avoid camera shake could admittedly have factored in. However, the search to lock on, to me, indicated that with the Kenko there was an issue. Without the Kenko, it locked on and held the confirmation light in the VF immediately.

The top image has sharp focus on the back rim of the glass. The bottom image has a lot of shake and looks worse. I don't think this was a representative test.

I believe the discussion of whether or not they worked was more absolute than focus accuracy. I think for some people, the combination flat doesn't work. Also, it's worth noting that the instructions say to mount the extender on the lens first and then put the combination on the body. While switching through the lenses I tested, I was just removing the lens from the extender while leaving it attached to the body. While the lens was off and the extender was still on the body, the camera's red light would blink even though the power was off. So, it's probably best to follow the instructions and mount the extender to the lens first.

Here's a sequence I did with my new 5D Mark III recently at Red Rocks Park, west of Denver. I use a hilltop radio tower and facility as a good lens testing target as it has lots of thin wires etc good for resolution testing. These were all on a tripod, but center spot auto-focus was used, no manual focus, and the auto-focusing seemed to be on the money and pretty quick, but admittedly it was a nice bright sunny day.

The first for reference is using the kit lens at 105mm, then the second is with my 70-300L @ 300mm, then the third with that lens with the Kenko 1.4X, making it 420 mm. I downsized these quite a bit for posting, but at full size, raw (especially with the new fixed DPP), these are pretty darn sharp.I reached the total attachment file size limit with these three, but I will post a follow-up with a 100% crop of the 420 mm shot. Comparing it back to the 105 mm image (which itself is already a ~ 2X magnification vs reality) I think the reach and image quality the Kenko is providing is quite good. Now if we could just figure out how to get it to work with some of the other lenses it doesn't want to play with, I'd be totally happy with it.

bchernicoff - I just read your post about the Kenko TC needing to be on the lens before mounting on the camera. I don't recall the mounting sequence I was doing the other day when I found it wouldn't work on four of my lenses (2 Canon and 2 Sigma). I just tried it per your suggestion with my Canon 100 2.8L macro and unfortunately, it still doesn't work - just locks up the camera requiring a battery removal to reset. That was one of the lenses that Kenko claims does work with the Mark III. I have a C-AF 1.4X Teleplus Pro 300 DGX model, recently purchased from Adorama.

I tried several of my telephotos with my 5D MK III using Canon TC's with the pins taped. Only my 70-200mm f/2.8 non IS actually worked well. I used it with 2X and 1.4X stacked. My 100-400mmL struggled with 1.4X at 400mm, my 70-200mml f/4 IS + 2X was a total failure, it just hunted, my 135mm L only found focus on distant objects.

Some camera / lens combinations may work, but different bodies may very well act differently.

Do any of you that are having problems live in the Washington DC area? You are welcome to try my teleconverter on your body and lenses and I would like to try yours. Maybe if we can find a pattern we can submit useful feedback to Kenko.